DAMASCUS, Syria -- Syrian government forces pushed into the ancient town of Palmyra, where Islamic State militants appeared on the verge of collapse Thursday, while in Iraq, a military spokesman announced the start of a long-awaited operation to recapture the IS-held northern city of Mosul.

The extremist group has been losing ground in Syria and Iraq for months under a stepped-up campaign of U.S.-led and Russian airstrikes, as well as ground assaults by multiple forces in each country.

The retaking of Palmyra -- a UNESCO world heritage site whose fall to the militants last May sent shock waves through archaeological circles and beyond -- would be a significant victory for the Syrian government. But the operation to unseat the group in Mosul, Iraq's second-largest city, is likely to take much longer and be far more difficult.

The advance on Palmyra came after government forces, backed by Russian airstrikes, managed to capture several hills and high ground around the town this week.

On Thursday, Syrian state TV broadcast footage of its reporter, embedded with the Syrian military, speaking live from the entrance of Palmyra and saying that as of midday, the fighting was concentrated near the famed archaeological site on the southwestern edge of the town. Cracks of gunfire and explosions echoed as the reporter spoke.

The fall of Palmyra to IS militants last year had raised concerns worldwide, and the destruction the extremists subsequently embarked upon sparked alarm and made international headlines. It was also a big blow to the government of Syrian President Bashar Assad, whose forces pulled out with apparently little resistance.

By nightfall, intense fighting was still taking place on the outskirts. Turkey-based activist Osama al-Khatib, who is originally from Palmyra, denied that Syrian troops had entered the town, and said the video seen on Syrian state TV was taken about three miles (five kilometres) from Palmyra.

Earlier in the day, Gov. Talal Barazi told The Associated Press from the nearby city of Homs that the Syrian army was clearing roads leading into the town of mines and explosives.

"We might witness in the next 48 hours an overwhelming victory in Palmyra," Barazi said, adding that "the army is advancing in a precise and organized way to protect what is possible of monuments and archaeological sites."

The Britain-based Syrian Observatory for Human Rights said Syrian troops and Shiite militiamen helping them on the ground were facing tough resistance from IS extremists as they try to penetrate the town's limits.

The Observatory, which monitors the Syrian conflict through a network of activists on the ground, said IS lost more than 200 militants since the government campaign to retake Palmyra began 17 days ago. It did not have figures for government losses.

The IS group instructed residents to leave the town Wednesday, according to a Palmyra native who asked not to be named. The town was mostly empty Thursday, save for IS fighters who were reported to be mining homes ahead of the advancing army.

Many of those who left sought refuge in IS-controlled cities in the country's north and east, including Deir el-Zour, which is also being contested between the extremist group and government forces, according to opposition media activists.

Affectionately known as the "bride of the desert," Palmyra had attracted tens of thousands of tourists to Syria every year.

But IS militants destroyed many of the town's Roman-era relics, including the 2,000-year-old Temple of Bel and the iconic Arch of Triumph, and also killed dozens of captive Syrian soldiers and dissidents in public slayings at the town's grand Roman theatre and other ruins.

Besides blowing up priceless archaeological treasures, IS demolished the town's infamous Tadmur prison, where thousands of Syrian government opponents had been imprisoned and tortured over the years.

The advance on Palmyra comes against the backdrop of Syrian peace talks underway in Geneva between representative of the Damascus government and the Western-backed opposition. The talks, which have been boosted by a Russia-U.S.-brokered cease-fire that has mostly held since late February, were to adjourn on Thursday -- without having achieved any apparent breakthroughs.

Meanwhile, in Iraq, government forces pushed Islamic State fighters out of several villages outside the town of Makhmour, southeast of the IS-held city of Mosul -- a move that Iraqi and coalition officials cast as the start of an operation to retake the strategic city.

Yet it also follows the death of a U.S. Marine stationed at a small U.S outpost close to Makhmour military base.

U.S.-led coalition spokesman U.S. Army Col. Steve Warren told reporters he believed the Islamic State group was specifically targeting the U.S. outpost and that IS attacks on the base had increased in recent weeks as Iraqi troops built up there and a larger number of U.S. and coalition forces moved in.

Regarding plans for a Mosul offensive, Warren said in a telephone interview that an Iraqi military buildup was still underway in the area.

"We announced several months ago that we had begun shaping operations for the eventual liberation of Mosul," Warren said. Thursday's "smaller ground operation conducted by the Iraqis is part of those shaping operations."

At a congressional hearing on Tuesday, Defence Secretary Ash Carter gave no indication that the Iraqis were ready for a full-scale counteroffensive. He said Iraq had "begun the shaping and isolation phase of the operation to collapse ISIL's control over Mosul."

Iraqi forces retook several villages on the outskirts of Makhmour early Thursday and hoisted the Iraqi flag there, according to the spokesman for the Joint Military Command, Brig. Gen. Yahya Rasool.

While the territorial gain does little for an eventual assault on Mosul, which U.S. and Iraqi officials recently said would take many months, it could push the front line between Iraqi and IS forces away from the Makhmour base.

The small U.S. artillery outpost near Makhmour has expanded the number and combat exposure of American troops in the country as Iraqi security forces prepare for a counteroffensive to retake Mosul, which fell to IS during the militants' June 2014 onslaught that captured large swaths of northern and western Iraq and neighbouring Syria.